Are there other genes besides Harlequin that modify Merle?

Only one merle modifier has been found so far: the Harlequin gene, which is found exclusively in the Great Dane breed.

While the sources explicitly state that Harlequin is the only discovered merle modifier, they do make a brief, somewhat contradictory passing reference to “other merle modifiers.” When explaining the Harlequin gene’s unique ability to affect red pigment (phaeomelanin), the text notes that it alters the entire coat, “not just eumelanin (black, liver, blue, isabella) like other merle modifiers”.

Despite this allusion, Harlequin is the only specific merle modifier identified and named in the provided material.

It is also worth noting that the Merle gene itself can produce different visual patterns (such as cryptic merle, dilute merle, or classic merle) based on the length of the genetic insertion within the SILV pigment gene. However, these differing insertion lengths are variations of the Merle gene itself, rather than separate modifying genes.